U.S. patent number 7,239,104 [Application Number 11/243,018] was granted by the patent office on 2007-07-03 for position-dependent friction compensation for steering systems.
This patent grant is currently assigned to ZF Lenksysteme GmbH. Invention is credited to Michael Bischofberger, Arnulf Heilig, Stephan Hiegler, Dietmar Hiller.
United States Patent |
7,239,104 |
Heilig , et al. |
July 3, 2007 |
Position-dependent friction compensation for steering systems
Abstract
A method is for compensating for a rotor angle deviation of a
motor, which may be used as an actuator, e.g., as a servo actuator,
in a steering system. The rotor angle deviation is compensated for
by a piecewise linearized control of the difference between a
desired rotor angle, which is based on a manual torque and a stored
rotor angle, and a measured rotor angle, a control factor of the
control being variable as a function of the control range.
Inventors: |
Heilig; Arnulf (Schwaebisch
Gmuend, DE), Hiegler; Stephan (Schwaebisch Gmuend,
DE), Bischofberger; Michael (Schwaebisch Gmuend,
DE), Hiller; Dietmar (Heuchlingen, DE) |
Assignee: |
ZF Lenksysteme GmbH
(Schwaebisch Gmuend, DE)
|
Family
ID: |
36062920 |
Appl.
No.: |
11/243,018 |
Filed: |
October 3, 2005 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20060076916 A1 |
Apr 13, 2006 |
|
Foreign Application Priority Data
|
|
|
|
|
Oct 2, 2004 [DE] |
|
|
10 2004 048 107 |
|
Current U.S.
Class: |
318/561; 318/609;
318/632 |
Current CPC
Class: |
B62D
5/0463 (20130101); B62D 5/0466 (20130101); B62D
6/008 (20130101) |
Current International
Class: |
B62D
5/04 (20060101) |
Field of
Search: |
;318/488,489,560,561,565,568.22,609-611,619,626,632
;180/6.28,443 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
199 20 975 |
|
Apr 2000 |
|
DE |
|
199 56 713 |
|
Jun 2000 |
|
DE |
|
100 51 864 |
|
Apr 2002 |
|
DE |
|
102 21 678 |
|
Dec 2003 |
|
DE |
|
Primary Examiner: Ro; Bentsu
Attorney, Agent or Firm: Kenyon & Kenyon LLP
Claims
What is claimed is:
1. A method for compensating for a rotor angle deviation of a
motor, comprising: piecewise linearized controlling of a difference
between a desired rotor angle and a measured rotor angle, the
desired rotor angle being based on a manual torque on a steering
handle and a stored rotor angle, a control factor of the
controlling being variable as a function of a control range.
2. The method according to claim 1, wherein the motor includes an
actuator in a steering system.
3. The method according to claim 1, wherein the control factor is
variable by a gradient change as a function of the control
range.
4. The method according to claim 1, wherein the controlling
includes breaking off the compensation for the rotor angle
deviation in the event that the compensation exceeds the desired
rotor angle.
5. The method according to claim 1, wherein the controlling
including compensating for all friction-related deviations of the
rotor angle under influences of the manual torque.
6. The method according to claim 1, wherein the controlling is
performed by a controller that includes at least one of (a) a
P-controller, (b) an I-controller and (c) a PI-controller.
7. The method according to claim 6, wherein a controlled system of
the I-controller is provided with a maximum control factor for
input variables that are quantitatively far from zero and is
provided with variable, quantitatively decreasing control factors
in an input variable range that is quantitatively near zero.
8. The method according to claim 1, further comprising influencing
a manipulated variable by a value limiter within an admissible
maximum range of values.
9. The method according to claim 8, wherein the value limiter is
linear within a first range and limited to the maximum manipulated
variable within a second range and a third range.
10. The method according to claim 1, further comprising
quantitatively limiting the manual torque to a maximum value.
11. The method according to claim 1, wherein the controlling sets
in in accordance with a change in the manual torque.
12. The method according to claim 1, wherein the controlling sets
in only when the manual torque exceeds a limiting value.
13. The method according to claim 1, further comprising determining
a desired rotor angle deviation from a difference of the manual
torque with respect to a previously stored manual torque,
multiplied by a gear ratio and divided by a factor for a system
stiffness.
14. The method according to claim 1, further comprising selecting a
first control if the manual torque is above a first threshold value
and selecting a second control if a magnitude of the manual torque
having a negative sign is above a second threshold value.
15. The method according to claim 14, wherein the first control
includes a positive compensation control.
16. The method according to claim 14, wherein the second control
includes a negative compensation control.
17. The method according to claim 14, wherein the first threshold
value and the second threshold value are quantitatively
identical.
18. A steering system, comprising: a device adapted to perform
piecewise linearized controlling of a difference between a desired
rotor angle and a measured rotor angle, the desired rotor angle
being based on a manual torque on a steering handle and a stored
rotor angle, a control factor of the controlling being variable as
a function of a control range.
19. The steering system according to claim 18, wherein the steering
system is arranged as a steering system for a motor vehicle.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority to Application No. 10 2004
048 107.5, filed in the Federal Republic of Germany on Oct. 2,
2004, which is expressly incorporated herein in its entirety by
reference thereto.
FIELD OF THE INVENTION
The present invention relates to a method for compensating for a
rotor angle deviation of a motor and to a steering system.
BACKGROUND INFORMATION
Steering systems such as electronic power steering systems, for
example, exhibit deviations between the specified torque determined
by the driver of the vehicle and the rotor angle actually set by
the steering system. The torque, also called manual torque, is
introduced into the steering system via a steering handle such as a
steering wheel or a joystick and the like. A desired rotor angle
(desired RW) is derivable from the manual torque. In an idealized
manner, a linear relationship is assumed between the manual torque
and the desired rotor angle. In conventional steering systems, the
manual torque is transmitted via a torsion element known as a
torsion bar (TB). The driver of the vehicle is supported by an
electrical or hydraulic motor or actuator such that the manual
torque to be introduced may be lower. The actuator transmits a
rotor angle (RW) onto an actuator shaft. In the process, however,
the steering system does not follow the specified manual torque
completely. The deviations are attributed to numerous causes.
Generally, the deviations are attributed to static deviations and
dynamic deviations, which, being system-related, are sought in
static frictions, in a hysteresis behavior of the steering system,
in liquid friction losses, in velocity losses and many other
causes.
German Published Patent Application No. 199 56 713 describes an
electric power steering device, the control unit of which
calculates a current control value for the motor of the power
assisted steering device. Deviations of the specified current
control value from the actual power steering device control are
attributed to additional loads, which are caused by feedback
effects of the roadway surface on the rack-and-pinion steering
gear. The feedback effects are to be absorbed with the aid of an
additional element, an elastic body.
U.S. Patent Application Publication No. 2003/006088 describes a
compensation table for the kinetic friction being stored in the
engine control unit.
A similar approach is described in German Published Patent
Application No. 102 21 678, which attributes the friction in the
steering system to a hysteresis torque, which is to be taken into
account in the desired torque input. The hysteresis characteristic
curve is ascertained as a function of the non-compensated desired
torque.
German Published Patent Application No. 199 20 975 subdivides the
causes for the friction losses in a more differentiated manner.
Five different kinds of friction are distinguished and calculated
in terms of control engineering. For this purpose an estimated
value is assumed for the static friction. The control provided thus
estimates the system deviation of the steering, which has a
separately energized DC motor as an actuator.
On the whole, the foregoing steering systems represent an attempt
to improve the feel of the steering for a driver of the vehicle.
Conventional friction compensations partly have the tendency to
overcompensate in the case of steering systems that have little
friction.
SUMMARY
An example embodiment of the present invention may provide
optimized friction compensation for steering systems.
Since the rotor angle deviation of the motor used in a steering
system is controlled in a compensating manner via a piecewise
linearized control on the basis of a desired rotor angle and the
measured rotor angle, whereby at least of the control factors of
the controls is changed as a function a the control range, the
control of the steering system may be optimized in the operation of
a steering system according to the method of an example embodiment
of the present invention. The term "control range" refers to the
deviation to be controlled. The control, which operates with actual
measured values of the steering system, determines the required
compensation. An overcompensation may be clearly reduced if not
avoided.
One of the control factors of the control may be changed by a
gradient change as a function of the control range. The gradient
change may always provide an optimum control factor for the current
rotor angle position. It changes continuously within an admissible
range of values. If only slight adjustments remain to be made, then
the control factor is changed such that a manipulated variable of
the control is adjusted only minimally.
According to a design of the control loop of the steering system,
the control may be designed such that, when the compensation
exceeds the desired rotor angle, the control breaks off the
compensation for the rotor angle deviation. This may prevent
overcompensation, the so-called overswinging of the control.
Steering systems that are only slightly affected by friction are
therefore not overcompensated.
In contrast to conventional, very complex control systems, which
may make all sorts of estimates using many input variables, the
steering system makes do with one single control, which compensates
for all friction-related deviations of the rotor angle when a
manual torque is applied. The degree of complexity may be reduced,
which may have advantageous effects on the stability and the
mutual, reinforcing influence.
The controller deliberately has ranges of values in which it no
longer operates in a linear manner. It is linearized in a piecewise
manner. The linear share of the control may include a controller,
which includes at least one controller either of a P-type or of an
I-type, e.g., a PI-controller. Using a P-controller, the rotor
angle deviation may be quickly eliminated. A PI-controller is used
to reduce the system deviation. If the control factor of the
I-controller is adjustable, then this may reduce the variability,
the overswinging or overcompensating tendency. The variability of
the I-controller may be designed such that the control factor of
the I-controller in quantitative terms is provided with a maximum
control factor in the case of input variables that are in
quantitative terms far from zero, and that the controlled system
may be provided with variable, that is to say, quantitatively
decreasing control factors in an input variable range that is
quantitatively near zero. With the quantitative delimitation of the
control factor, the control fundamentally may move within a
technically meaningful range of values and may not drift into an
extreme position.
As a further measure for maintaining the controller within a range
of values utilizable by the actuator, the values of the manipulated
variable of the control may be limited. The compensation for the
rotor angle deviation is limited within an admissible maximum range
of values by influencing the manipulated variable via a value
limiter. The value limiter has at least three sections or ranges.
Within a first range, it operates in a linear manner, and within a
second and a third range, the manipulated variable is
quantitatively limited to the maximum manipulated variable.
As particular stabilizing measures may be taken on the output side
of the controller, the method may also be stabilized by measures
for the input variables. Thus in an exemplary embodiment, the
manual torque may be quantitatively limited to a maximum value. The
control may set in with any change of the manual torque. It may be
provided, however, for the control to operate only once a limiting
value of the manual torque has been exceeded and to set in only
afterwards. Minimal changes may thus be absorbed and the control
may not correct itself permanently.
The method may be based on the assumption that a desired rotor
angle deviation is determined from the difference of the manual
torque with respect to a previously stored manual torque,
multiplied by a gear ratio and divided by a factor for the system
stiffness.
A first control, the positive compensation control, may be selected
if the manual torque is above a threshold value, and a second
control, the negative compensation control, may be selected if the
magnitude of the manual torque having a negative sign is above a
threshold value. For this purpose, the threshold values of the
manual torque may be quantitatively identical for the positive and
negative compensation.
The foregoing may be used in a steering system, e.g., for motor
vehicles such as passenger cars. Their friction-dependent rotor
angle deviation may operate according to a method according to an
example embodiment of the present invention.
According to an example embodiment of the present invention, a
method for compensating for a rotor angle deviation of a motor
includes: piecewise linearized controlling of a difference between
a desired rotor angle and a measured rotor angle, the desired rotor
angle being based on a manual torque on a steering handle and a
stored rotor angle, a control factor of the controlling being
variable as a function of a control range.
The motor may include an actuator in a steering system.
The control factor may be variable by a gradient change as a
function of the control range.
The controlling may include breaking off the compensation for the
rotor angle deviation in the event that the compensation exceeds
the desired rotor angle.
The controlling may include compensating for all friction-related
deviations of the rotor angle under influences of the manual
torque.
The controlling may be performed by a controller that includes at
least one of (a) a P-controller, (b) an I-controller and (c) a
PI-controller.
A controlled system of the I-controller may be provided with a
maximum control factor for input variables that are quantitatively
far from zero and may be provided with variable, quantitatively
decreasing control factors in an input variable range that is
quantitatively near zero.
The method may include influencing a manipulated variable by a
value limiter within an admissible maximum range of values.
The value limiter may be linear within a first range and limited to
the maximum manipulated variable within a second range and a third
range.
The method may include quantitatively limiting the manual torque to
a maximum value.
The controlling may set in in accordance with a change in the
manual torque.
The controlling may set in only when the manual torque exceeds a
limiting value.
The method may include determining a desired rotor angle deviation
from a difference of the manual torque with respect to a previously
stored manual torque, multiplied by a gear ratio and divided by a
factor for a system stiffness.
The method may include selecting a first control if the manual
torque is above a first threshold value and selecting a second
control if a magnitude of the manual torque having a negative sign
is above a second threshold value.
The first control may include a positive compensation control.
The second control may include a negative compensation control.
The first threshold value and the second threshold value may be
quantitatively identical.
According to an example embodiment of the present invention, a
steering system includes: a device adapted to perform piecewise
linearized controlling of a difference between a desired rotor
angle and a measured rotor angle, the desired rotor angle being
based on a manual torque on a steering handle and a stored rotor
angle, a control factor of the controlling being variable as a
function of a control range.
The steering system may be arranged as a steering system for a
motor vehicle.
Example embodiments of the present invention are described in more
detail with reference to the appended Figures
BRIEF DESCRIPTION OF THE DRAWINGS.
FIG. 1 is a state diagram of a control according to an example
embodiment of the present invention.
FIG. 2 illustrates a method for compensating for a rotor angle
deviation for positive rotor angle deviations.
FIG. 3 illustrates a method for compensating for a rotor angle
deviation for negative rotor angle deviations.
DETAILED DESCRIPTION
FIG. 1 illustrates the sequence of a control for steering systems
according to an example embodiment of the present invention in the
form of a state diagram. In state 1, the current variables are
first saved by a recopying process 10 in a recopying and
initialization step. Afterwards, a check is performed by a
comparison of values as to whether the manual torque introduced,
that is, the torque that a driver of the vehicle intends to
transmit to the steering system as the selected torque, is to
initiate a further processing step in a new state, the control
state 3 and the control state 5, so as to result in a control 38,
58, the actual compensation control. Within the scope of the
recopying process 10, the values of the rotor angle (RW), of the
manual torque (TBT) and of the desired rotor angle (Desired RW or
DeRW) are described. The rotor angle (RW) and the manual torque
(TBT) are described using the current measured values. The desired
rotor angle (DeRW) is set to 0 so that within the context of
control 38, 58 it is then able to receive the calculated value. If
the manual torque is greater than a limiting manual torque value 12
(ZeroTBT), the system branches into the positive control state 3.
If the absolute value of the manual torque is greater than a
limiting manual torque value 14, the system branches into the
negative control state 5. If the limiting manual torque values
(ZeroTBT) are undershot, then the control system remains in state
1, which may also be referred to as an archiving and initialization
state for the control.
The continuing specification considers a controller according to
FIG. 2 and FIG. 3, which includes an integrator in the form of an
I-controller 124, 224 and a proportional controller (P-controller)
136, 236, and which by an addition in adder 144, 244 forms a
PI-controller. It should be understood that example embodiments of
the present invention are not limited only to PI-controllers, but
that in their place PID-controllers or any other kind of control
factor-adaptive controller type such as a pure P-controller or a
controller of a higher order may be provided. For simplicity, the
further remarks are presented for a PI-controller, including an
I-controller 124, a P-controller 136 and an adder 144, having
positive integration and compensation, or for a PI-controller,
including an I-controller 224, a P-controller 236 and an adder 244,
having negative integration and compensation.
The two states 3, 5 illustrated in FIG. 1, which yield the positive
control state for compensating for a positive friction value, the
friction compensation manipulated variable (FrictionComp) 150, and
the negative control state for compensating for a negative friction
value, the friction compensation manipulated value (FrictionComp)
250, are similar in structure. The different sign in the manual
torque (TBT), however, is taken into account by sign multiplication
by (-1) or by a reversal of the comparison operators. In states 3,
5, an ascertainment is made in a first comparison 30, 50 as to
whether the I-share of the position controller (IPart) is
quantitatively higher than a specified I-share for a zero limit
(ZeroPart). If the I-share (IPart) is quantitatively above an
I-share limit value (ZeroIPart), then the respective compensation
control 38, 58 is activated. If the compensation limit for the
compensation (TBTReady) exceeds 32 or undershoots 52 the manual
torque (TBT) and the limit for the lower manual torque 34, 54 is
undershot, then the positive 38 or negative compensation control 58
may be started in states 3, 5. Otherwise a limiting value
persistence 70 is checked in safety state 7 or a transition is made
from control state 3 to control state 5 or vice versa following a
storage step of variables 36, 56.
Favorable limits for a stable state change are limits of
approximately 0.1 Nm for example. Below a manual torque (TBT) of
approximately 0.1 Nm, the control assumes that the driver of the
vehicle did not intend to perform a driving maneuver. As a result,
the vehicle becomes more stable overall when there are smaller
manual torque fluctuations in straightforward driving. The two
control according to FIG. 2 and FIG. 3 are similar. Due to the
different signs of the variable of the measured rotor angle
(wrsRotrangle) 110, 210, of the manual torque (mstTorsionBarTorque)
102, 202 and of the stored rotor angle (StoredRW) 100, 200, the
I-controller 124, 126 illustrated in FIG. 2 or the I-controller
224, 226 illustrated in FIG. 3 and the P-controller 136 illustrated
in FIG. 2 or the P-controller 236 illustrated in FIG. 3 are
established using positive and negative values. The value of
I-controllers 124, 126, 224, 226 is limited in its maximum I-value
(IPart) to a maximum value by the limiting value 128, 228 in the
limiter of I-controller 126, 226. From the difference between the
subtracter 112, 212 of the manual torque (TorsionBarTorque) 102,
202 and the stored manual torque (StoredTBT) 104, 204, a rotor
angle, which may be added to the stored rotor angle (StoredRW) 100,
200 by an adder 118, 218, is determined using a position factor
(TBTToPos) 106, 206 and an optional value limiter 116, 216 having a
limiting value (maxOffsetangle) 100, 200.
Following the addition, controller 38, 58 has the desired rotor
angle (DesiredRW) 120, 210 available, from which the measured rotor
angle (Rotorangle) 110, 210 is subtracted by a subtracter 122, 222.
The signal of subtracter 122, 222 is applied parallel to an
I-controller including the elements 124, 126, 224, 226 and to a
P-controller 136, 236. The individual signals after the
I-controller, including the elements 124, 126, 224, 226, and after
the P-controller 136, 236 are added to form a signal of a
PI-controller via an adder 144, 244. Multipliers 130, 140, 230,
240, 132, 134, 232, 234 are provided for value adjustment. At the
same time, value limiters 146, 148, 246, 248 may stabilize the
control and may eliminate its tendency to oscillate.
The measures of stabilization by splitting signals and limiting
signals may be optional and may not need to be present for a simple
implementation of a control according to an example embodiment of
the present invention. Behind adder 144, 244, the friction
compensation manipulated value 150, 250 may be read off, which is
then applied to an actuator of the steering system.
REFERENCE NUMERAL LISTING STATE
3 control state 5 control state 7 safety state 10 recopying and
initialization step 12 limiting manual torque value comparison 14
limiting manual torque value comparison 30 first comparison 32
compensation limit comparison 34 lower manual torque comparison 36
variables storage step 38 compensation control 50 first comparison
52 compensation limit comparison 54 lower manual torque 56
variables storage step 58 compensation control 70 limiting value
persistence 100 stored rotor angle 102 manual torque 104 stored
manual torque 106 position factor 108 limiting value 110 rotor
angle 112 substracter 114 multiplier 116 value limiter 118 adder
120 rotor angle 122 substracter 124 I-controller 126 I-controller
128 limiting value 130 multiplier 132 multiplier 134 multiplier 136
proportional controller 140 multiplier 144 adder 146 value limiter
148 value limiter 150 friction compensation manipulated value 200
stored rotor angle 202 manual torque 204 stored manual torque 206
position factor 208 limiting value 210 rotor angle 212 substracter
214 multiplier 216 value limiter 218 adder 220 rotor angle 222
substracter 224 I-controller 226 I-controller 228 limiting value
230 multiplier 232 multiplier 234 multiplier 236 proportional
controller 240 multipliers 244 adder 246 value limiter 248 value
limiter 250 friction compensation manipulated value
* * * * *